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Drug Resistance

As HIV multiplies in the body, the virus sometimes mutates (changes form) and produces variations of itself. Variations of HIV that develop while a person is taking HIV medicines can lead to drug-resistant strains of HIV.

With drug resistance, HIV medicines that previously controlled a person’s HIV are not effective against new, drug-resistant HIV. In other words, the HIV medicines can't prevent the drug-resistant HIV from multiplying. Drug resistance can cause HIV treatment to fail.

A person can initially be infected with drug-resistant HIV or develop drug-resistant HIV after starting HIV medicines.

Medication adherence—taking HIV medicines every day and exactly as prescribed—reduces the risk of drug resistance.

What is HIV drug resistance?

Once a person has HIV, the virus begins to multiply (make copies of itself) in the body. As HIV multiplies, it sometimes mutates (changes form) and produces variations of itself. Variations of HIV that develop while a person is taking HIV medicines can lead to drug-resistant strains of HIV.

With drug resistance, HIV medicines that previously controlled the person’s HIV are not effective against the new, drug-resistant HIV. In other words, the HIV medicines can’t prevent the drug-resistant HIV from multiplying. Drug resistance can cause HIV treatment to fail.

Drug-resistant HIV can spread from person to person. People initially infected with drug-resistant HIV have drug resistance to one or more HIV medicines even before they start taking HIV medicines.

How does poor medication adherence increase the risk of drug resistance?

Medication adherence means taking HIV medicines every day and exactly as prescribed. HIV medicines prevent HIV from multiplying. Skipping HIV medicines allows HIV to multiply, which increases the risk that the virus will mutate and produce drug-resistant HIV.

As a result of drug resistance, one or more HIV medicines in a person’s HIV regimen may no longer be effective.

What is cross resistance?

Cross resistance is when resistance to one HIV medicine causes resistance to other medicines in the same HIV drug class. (HIV medicines are grouped into drug classes according to how they fight HIV.) As a result of cross resistance, a person’s HIV may be resistant even to HIV medicines that the person has never taken. Cross resistance limits the number of HIV medicines available to include in an HIV regimen.

What is drug-resistance testing?

Drug-resistance testing is done to identify which, if any, HIV medicines won’t be effective against a person’s strain of HIV. Drug-resistance testing is done using a sample of blood.

Drug-resistance testing is done when a person first begins receiving care for HIV infection. Resistance testing should be done whether the person decides to start taking HIV medicines immediately or to delay treatment. If treatment is delayed, resistance testing may be repeated when HIV medicines are started.

Drug-resistance testing done before a person starts HIV medicines for the first time can show whether the person was initially infected with a drug-resistant strain of HIV. Drug-resistance testing results are used to decide which HIV medicines to include in a person’s first HIV regimen.

After treatment is started, drug-resistance testing is repeated if viral load testing indicates that a person’s HIV regimen isn’t controlling the virus. If drug-resistance testing shows that the HIV regimen isn’t effective because of drug resistance, the test results can be used to select a new HIV regimen.

Drug-resistance testing is also recommended for all pregnant women with HIV before starting HIV medicines and also in some pregnant women already taking HIV medicines. Pregnant women will work with their health care providers to decide if drug-resistance testing is needed.

How can a person taking HIV medicines reduce the risk of drug resistance?

Adherence to an effective HIV treatment regimen reduces the risk of drug resistance.

Here are some tips on medication adherence for people living with HIV:

Once you decide to start treatment, work closely with your health care provider to choose an HIV regimen that suits your needs. A regimen that meets your needs will make adherence easier. Tell your health care provider about any issues that can make adherence difficult. For example, tell your health care provider if you have a busy schedule that makes it hard to take medicines on time or lack health insurance to cover the cost of HIV medicines. Your health care provider can recommend resources to help you address any issues before you start taking HIV medicines.

When you start treatment, closely follow your HIV regimen. Take your HIV medicines every day and exactly as prescribed. Use medication aids such as a 7-day pill box or pill diary to stay on track. Download the AIDSinfo Drug Database app to set daily pill reminders.

Keep your medical appointments so that your health care provider can monitor your HIV treatment. Appointments are a good time to ask questions and ask for help to manage problems that make it hard to follow an HIV regimen.